1. Field of the Invention
The present invention relates generally to improvements in seed and seed-related products, processes for making such products, and processes for establishing and improving seed beds. This invention is also directed at improving seed establishment on post-fire water-repellent soil.
2. Background Art
Effective reseeding efforts are important for establishing desirable plant species on agricultural, rangeland, forested land, urbanized areas (i.e. turf), and dry spots. However, these efforts are often encountered with specific problems that include the development of hydrophobic soil layers that prevent effective seed germination and plant establishment. For example, in the western United States, the widespread expansion and stand infilling by piñon (Pinus) and juniper (Juniperus) (P-J) species into grassland and sagebrush communities constitutes one of the greatest modern-day afforestations. Since European settlement of the Western U.S., P-J species have expanded their range to more than 40 million hectares (Romme, W. H., C. D. Allen, J. D. Bailey, W. L. Baker, B. T. Bestelmeyer, P. M. Brown, K. S. Eisenhart, M. L. Floyd, D. W. Huffman, B. F. Jacobs, R. F. Miller, E. H. Muldavin. T. W. Swetnam, R. J. Tausch, and P. J. Weisberg. 2009. Historical and modern disturbance regimes, stand structures, and landscape dynamics in pinon-juniper vegetation of the Western United States. Rangeland Ecology and Management 62:203-222). This ecosystem shift has resulted in negative impacts to soil resources, plant community structure and composition, forage quality and quantity, water and nutrient cycles, wildlife habitat, and ecological biodiversity. As P-J woodlands mature, increased fuel loads and canopy cover can lead to large-scale, high intensity crown-fires (Miller, R. F., R. J. Tausch, D. Macarthur, D. D. Johnson, S. C. Sanderson. 2008. Development of post settlement pifion-juniper woodlands in the Intermountain West: a regional perspective. USDA Forest Service, Research Paper Report RMRS-Rp-69). After a fire, the ability of desirable plant communities to recover depends on the extent to which physical and biological processes controlling ecosystem function have been altered, both prior to and as result of the fire (Briske, D. D., S. D. Fuhlendorf, and F. E. Smeins. 2005. A unified framework for assessment and application of ecological thresholds. Rangeland Ecology and Management 59:225-236).
Like P-J woodlands, these cultivated and wildlands may experience similar alterations to both physical and biological structure and process. Reseeding techniques are needed that increase plant establishment, in particular when associated with altered soil properties such as hydrophobic layers. In the case of P-J forests, low seed establishment in hydrophobic soils can lead to undesirable ecological thresholds. When this threshold is crossed, the recovery of desirable species may not be possible without direct human intervention. If sites remain disturbed and unvegetation for a year or more, sites can transition into a secondary state of weed dominance, which then promotes more frequent fire return intervals and decreased native plant establishment, further impairing vital ecosystem function (Young, J. A., and R. A. Evans. 1978. Population dynamics after wildfires in sagebrush grasslands. Journal of Range Management 31:283-289).
Restoring desired species, recovering natural processes, and preventing movement toward undesirable thresholds is accomplished with the successful establishment of desirable vegetation. In the past, land managers have typically selected introduced species such as crested wheatgrass (Agropyron cristatum (L.) Gaertn.) and forage kochia (Bassia prostrata (L.) A. J. Scott). These species often have more consistent establishment, lower costs, better weed competition, and improved livestock forage quality. Currently, many federal and state organizations are increasing the use of native plant materials in place of introduced species in an effort to reinstate ecosystem processes and improve species diversity (Thompson, T. W., B. A. Roundy, E. D. McArthur, B. D. Jessop, B. Waldron, J. N. Davis. 2006. Fire rehabilitation using native and introduced species: A Landscape Trial. Rangeland Ecology and Management 59:237-248), however, these species are costly and establishment success is typically less than desirable. Therefore, the use of native species in reseeding efforts typically increases project costs while decreasing the likelihood of successfully-establishing a functional community. These issues reduce the desire of land managers to include native plant materials in rehabilitation projects.
To improve the success of reseeding efforts, several mechanical and non-mechanical treatments have been proposed with varying degrees of effectiveness. For example, aerial reseeding followed by anchor chaining is commonly practiced for post-fire rehabilitation of P-J woodlands. Although this form of mechanical treatment has been shown to be successful in many situations, the additional disturbance may increase risk of soil erosion by wind and water. Furthermore, economic, cultural, and topographic constraints (i.e. soils are too rocky or steep) prevent the use of this mechanical treatment on a significant portion of the landscape.
When restoration practices fail, ecological resilience is compromised, and soil loss, weed invasion, and other factors act as triggers that initiate feedback shifts that carry a site across ecological thresholds to undesirable alternate stable states. Land managers throughout the Intermountain West are calling for new techniques that improve establishment of native plant materials to restore habitats and to prevent subsequent weed dominance.
In order to develop successful restoration approaches, it is critical that the mechanisms which impair vegetation establishment or recovery and the conditions that develop prior to disturbance which lead to crossing ecological thresholds are understood. If the state of an individual site is known in relation to ecological thresholds and possible transitions to other states, capital can be correctly allocated to sites in transition, in order to promote the system's natural ability to recover. Furthermore, an understanding of the mechanisms that prevent recovery will allow the development of resilience-based approaches that promote recovery of ecosystem process and function (Briske, D. D., S. D. Fuhlendorf, and F. E. Smeins. 2005. A unified framework for assessment and application of ecological thresholds. Rangeland Ecology and Management 59:225-236).
Hydrophobicity, or soil water repellency, is one factor that may significantly limit recovery of plant communities and enhance weed dominance within P-J dominated systems after fire. Soil water repellency is commonly found in arid and semi-arid ecosystems. Post-fire patterns of soil water repellency have been shown to be highly correlated with decreased soil water content, infiltration, and revegetation success (Madsen, M. D. 2010. Influence of soil water repellency on post-fire revegetation success and management techniques to improve establishment of desired species. Dissertation, Brigham Young University, Provo, Utah). We hypothesize that post-fire WR acts as a temporal ecological threshold by impairing establishment of desired species within the first few years after a fire, which then leaves resources available for weed invasion after WR has diminished. Better knowledge of WR in P-J ecosystems is necessary to guide management actions as these woodlands continue to encroach, infill, and mature throughout their adaptable range (Miller et al. 2008).
Restoration approaches which focus on ameliorating WR could potentially improve the success of native plant materials following reseeding efforts while simultaneously decreasing runoff and soil erosion, and preventing weed domination. Use of commercially available surface active agents (wetting-agents or surfactants) may provide an alternative restoration approach where WR inhibits site recovery. A wide variety of ionic and nonionic wetting-agents are produced commercially, ranging from simple dish soaps to sophisticated polymers chemically engineered to overcome WR. Wetting-agents are generally organic molecules that are amphiphilic (hydrophobic tails and hydrophilic heads). While wetting agents have different modes of action, in the case of soil applications the hydrophobic tail of the wetting-agent chemically bonds to the non-polar water repellent coating on the soil particle, while the hydrophilic head of the molecule attracts water molecules, thus rendering the soil wettable.
Small plot, post-fire research projects, located in the mountains of southern California, have shown that the application of wetting-agents after a fire can reduce soil erosion and improve vegetation establishment (Osborn, J. F., R. E. Pelishek, J. S. Krammes, and J. Letey. Soil wettability as a factor in erodibility. Soil Science Society of America Proceedings 28:294-295). These studies suggest that wetting-agent applications can be a successful post-fire treatment. While wetting-agents have not been used in wildland systems since the 1970's, they have been extensively used and further developed within various aspects of the agricultural industry, with most applications in turf grass systems (Kostka, S. J. 2000. Amelioration of water repellency in highly managed soils and the enhancement of turfgrass performance through the systematic application of surfactants. Journal of Hydrology 231-232:359-368). Subsequently, the effectiveness of these chemicals in overcoming soil WR has been improved. The development of these wetting-agents may provide an innovative approach for alleviating the effects of WR on germination and establishment of native vegetation species, thus allowing them to better compete with invasive annual weed species such as cheatgrass (Bromus tectorum L.).
The primary objectives of this research were to quantify within a glasshouse setting: 1) the extent that soil water repellency influences emergence and growth of the non-native bunchgrass crested wheatgrass (Agropyron cristatum (L.) Gaertn., and native bunchgrass, bluebunch wheatgrass (Pseudoroegneria spicata (Pursh) A. Löve), both of which are commonly seeded for fire rehabilitation, in the Intermountain West, USA; and 2) determine the effects of the newly developed non-ionic wetting-agent “Soil Penetrant” (Aquatrols Inc., Paulsboro, N.J.) on WR and seedling growth to assess its potential use in wildfire rehabilitation of P-J ecosystems.
Water Repellence in Relation to Fire.
After a fire, the ability of ecosystem to recover is dependent on the extent to which ecological processes have been altered. Modification of the soil through the development of a hydrophobic layer is one alteration which can significantly limit site recovery. Wildland vegetation can create a hydrophobic layer in the first few centimeters of the soil profile.
During a fire, heat can volatilize organic substances within the litter and upper hydrophobic soil layers. These volatilized compounds then move downward into the soil, condensing within the cool underlying soil layers. This results in a wettable layer at the soil surface and an intensified hydrophobic zone a few centimeters below the soil surface. The development or enhancement of this hydrophobic layer has severe implications for revegetation success, runoff, and soil erosion. Seeds which germinate within the soils upper wettable layer typically desiccate, as a result of the water repellent layer disconnecting the seedling from the underlying soil moisture reserves (FIG. 2). The lack of seedling establishment allows for continued soil erosion and provides the opportunity for invasion of annual weeds in subsequent years, when sown seeds are no longer viable.
The arrangement of a wettable soil layer overlying a water repellent layer also has severe implications for water runoff and soil stability. During a rainfall event the upper wettable layer is quickly saturated due to the underlying water repellent layer impeding infiltration. On steep slopes, when this wettable layer becomes saturated from high intensity rainfall events, water, soil, and debris can quickly flow down slope, which causes site degradation and property damage if it is within the wildland urban interface.
Large amounts of public funds are spent each year on postfire rehabilitation treatments. Currently, post-fire rehabilitation treatments include providing immediately surface cover by straw mulching, hydromulching and other methods. However, these methods are expensive; for example straw mulching has been shown to range between $1000 per hectacre and $3000 per hectacre and hydromulching can range between $2350 per hectacre to $4700 per hectacre. Consequently, applying such strategies can be almost impractical at large scales. Thus, there is currently a need for effective postfire rehabilitation treatments which can be applied at the landscape scale which ameliorate the influence of hydrophobic soil and establish desirable plants back into the system.
Use of commercially available soil surfactants may provide an alternative postfire restoration approach where hydrophobicity and limited soil moisture availability are preventing site recovery. Soil surfactant molecules are hydrophobic on one end and hydrophilic on the other end. Upon entering the soil the hydrophobic end of the soil surfactant chemically attaches to the non-'polar water repellent coating on the soil particle; while the hydrophilic end of the agent is able to attract water molecules allowing soil moisture to be absorbed in the upper hydrophobic soil layers.
Various small plot postfire research projects located in the chaparral mountains of southern California have shown that the application of soil surfactants after a fire can reduce soil erosion and improve vegetation establishment. These studies suggest that the application of soil surfactants can be a successful postfire treatment. While soil surfactants have not been used in wildland systems since the 1970's, they have been extensively used and further developed in various aspects of the agricultural industry, with particular use in turf production. Subsequently, the effectiveness of these chemicals in diminishing soil hydrophobicity has been improved. The development of these soil surfactant products may provide an innovative approach for alleviating the effects of hydrophobicity on runoff and soil erosion, and allow native vegetation species, the ability to better compete with invasive annual weed species such as cheatgrass (Bromus tectorum). While these results are promising, application of soil amendments is typically not practical for the revegetation of wildland systems, due to the large areas and low economic value of the land to be treated. Commercially available soil surfactant products are particularly costly. Furthermore, the application of these chemicals to a wildland landscape is difficult at best.